package org.apache.solr.spelling.suggest.fst;

import org.apache.lucene.search.suggest.Lookup;
import org.apache.lucene.search.suggest.fst.FSTCompletionLookup;
import org.apache.solr.common.util.NamedList;
import org.apache.solr.core.SolrCore;
import org.apache.solr.spelling.suggest.LookupFactory;

/**
 * Factory for {@link FSTCompletionLookup}
 */
public class FSTLookupFactory extends LookupFactory {

    /**
     * File name for the automaton.
     */
    private static final String FILENAME = "fst.bin";
    /**
     * The number of separate buckets for weights (discretization). The more
     * buckets, the more fine-grained term weights (priorities) can be assigned.
     * The speed of lookup will not decrease for prefixes which have
     * highly-weighted completions (because these are filled-in first), but will
     * decrease significantly for low-weighted terms (but these should be
     * infrequent, so it is all right).
     *
     * <p>The number of buckets must be within [1, 255] range.
     */
    public static final String WEIGHT_BUCKETS = "weightBuckets";
    /**
     * If
     * <code>true</code>, exact suggestions are returned first, even if they are
     * prefixes of other strings in the automaton (possibly with larger
     * weights).
     */
    public static final String EXACT_MATCH_FIRST = "exactMatchFirst";

    @Override
    public Lookup create(NamedList params, SolrCore core) {
        int buckets = params.get(WEIGHT_BUCKETS) != null
                ? Integer.parseInt(params.get(WEIGHT_BUCKETS).toString())
                : 10;

        boolean exactMatchFirst = params.get(EXACT_MATCH_FIRST) != null
                ? Boolean.valueOf(params.get(EXACT_MATCH_FIRST).toString())
                : true;

        return new FSTCompletionLookup(buckets, exactMatchFirst);
    }

    @Override
    public String storeFileName() {
        return FILENAME;
    }
}
